Post-deposition treatment to enhance properties of Si-O-C low k films

ABSTRACT

A method for providing a dielectric film having enhanced adhesion and stability. The method includes a post deposition treatment that densifies the film in a reducing atmosphere to enhance stability if the film is to be cured ex-situ. The densification generally takes place in a reducing environment while heating the substrate. The densification treatment is particularly suitable for silicon-oxygen-carbon low dielectric constant films that have been deposited at low temperature.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/293,096, filed Nov. 12, 2002, entitled “Post-Deposition Treatment toEnhance Properties of Si—O—C Low k Films,” having Li-Qun Xia, FredericGaillard, Ellie Yieh, Tian H. Lim listed as coinventors; which is adivision of U.S. application Ser. No. 09/632,669, filed Aug. 7, 2000,now U.S. Pat. No. 6,486,061, issued Nov. 26, 2002. The disclosures ofU.S. Ser. Nos. 10/293,096 and 09/632,669 are herein incorporated hereinby reference in their entirety.

This application is related to U.S. application Ser. No. 09/625,911,filed Aug. 7, 2000; and to U.S. application Ser. No. 09/633,495, filedAug. 7, 2000, now U.S. Pat. No. 6,465,372, issued Oct. 15, 2002; and toU.S. application Ser. No. 09/633,196, filed Aug. 7, 2000, now U.S. Pat.No. 6,635,575, issued Oct. 21, 2003; and to U.S. application Ser. No.09/633,798, filed Aug. 7, 2000, now U.S. Pat. No. 6,528,116, issued Mar.4, 2003. Each of the Ser. Nos. 09/625,911, 09/633,495, 09/633,196 and09/633,798 applications listed above are assigned to Applied Materials,Inc., the assignee of the present invention and are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

The present invention relates to the formation of dielectric layersduring fabrication of integrated circuits on semiconductor wafers. Moreparticularly, the present invention relates to a method for providing adielectric film having a low dielectric constant that is particularlyuseful as a premetal or intermetal dielectric layer.

One of the primary steps in the fabrication of modern semiconductordevices is the formation of a thin film on a semiconductor substrate bychemical reaction of gases. Such a deposition process is referred to aschemical vapor deposition or “CVD.” Conventional thermal CVD processessupply reactive gases to the substrate surface where heat-inducedchemical reactions take place to produce a desired film. Plasma enhancedCVD techniques, on the other hand, promote excitation and/ordissociation of the reactant gases by the application of radio frequency(RF) or microwave energy. The high reactivity of the released speciesreduces the energy required for a chemical reaction to take place, andthus lowers the required temperature for such PECVD processes.

Semiconductor device geometries have dramatically decreased in sizesince such devices were first introduced several decades ago. Today'sfabrication plants are routinely producing devices having 0.25 μm andeven 0.18 μm feature sizes, and tomorrow's plants soon will be producingdevices having even smaller geometries. In order to further reduce thesize of devices on integrated circuits, it has become necessary to useconductive materials having low resistivity and insulators having a lowdielectric constant. Low dielectric constant films are particularlydesirable for premetal dielectric (PMD) layers and intermetal dielectric(IMD) layers to reduce the RC time delay of the interconnectmetalization, to prevent cross-talk between the different levels ofmetalization, and to reduce device power consumption. Undoped siliconoxide films deposited using conventional CVD techniques may have adielectric constant (k) as low as about 4.0 or 4.2. One approach toobtaining a lower dielectric constant is to incorporate fluorine in thesilicon oxide film. Fluorine-doped silicon oxide films (also referred toas fluorine silicate glass or—“FSG” films) may have a dielectricconstant as low as about 3.4 or 3.6. Despite this improvement, filmshaving even lower dielectric constants are highly desirable for themanufacture of integrated circuits using geometries of 0.18 μm andsmaller. Numerous films have been developed in attempts to meet theseneeds including: a spin-on glass called HSQ (hydrogen silsesqui-oxane,HSiO_(1.5)) and various carbon-based dielectric layers, such as paryleneand amorphous fluorinated carbon. Other low-k films have been depositedby CVD using an organosilane precursor and oxygen to form asilicon-oxygen-carbon (Si—O—C) layer.

While the above types of dielectric films are useful for someapplications, manufacturers are always seeking new and improved methodsof depositing low-k materials for use as IMD and other types ofdielectric layers. For example, after deposition at low temperature, asilicon carbon or Si—O—C film is often quite porous. Consequently, thefilm tends to absorb moisture. The absorbed moisture generally degradesthe properties of the film. In the case of a low-k film, moisture tendsto increase the dielectric constant of the film and is detrimental tofilm adhesion.

BRIEF SUMMARY OF THE INVENTION

The method of the present invention provides a new and improvedpost-deposition treatment process. The method of the present inventiondeposits and densifies and cures an insulating layer. Thepost-deposition densification treatment further enhances adhesion byreducing shrinkage of the deposited film. The post-depositiondensification takes place in a reducing environment. In one embodiment,the deposited film is treated in a reducing environment of ammonia forapproximately 1 to 5 minutes at a temperature of approximately 400° C.Curing can be done in either a vacuum or conventional furnaceenvironment. The densification is particularly useful for enhancing thestability of a film that is to be cured ex-situ, i.e. after removing thesubstrate from vacuum.

The densification is beneficial for films deposited by a low-temperatureCVD process. In one embodiment, the insulating layer is deposited from aprocess gas of ozone and an organosilane precursor having at least onesilicon-carbon (Si—C) bond. During the deposition process, the substrateis heated to a temperature less than about 250° C. In some embodiments,the organosilane precursor has a formula of Si(CH₃)_(x)H_(4-x) where xis either 3 or 4 making the organosilane precursor eithertrimethylsilane (TMS) or tetramethylsilane (T4MS). In other embodiments,the substrate over which the carbon-doped oxide layer is deposited isheated to a temperature of between about 100-200° C. and the depositionis carried out in a vacuum chamber at a pressure of between 1-760 Torr.

The method is particularly useful in the manufacture of sub-0.2 microncircuits as it can form a PMD or IMD film with a dielectric constantbelow 3.0. The film has good gap fill capabilities, high film stabilityand etches uniformly and controllably when subject to a chemicalmechanical polishing (CMP) step. The method is particularly useful when,for throughput reasons, the substrate containing the deposited film isremoved from vacuum for curing in a furnace.

These and other embodiments of the present invention, as well as itsadvantages and features, are described in more detail in conjunctionwith the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are vertical, cross-sectional views of one embodiment ofa chemical vapor deposition apparatus according to the presentinvention;

FIGS. 1C and 1D are exploded perspective views of parts of the CVDchamber depicted in FIG. 1A;

FIG. 1E is a simplified diagram of system monitor and CVD system 10 in amulti-chamber system, which may include one or more chambers;

FIG. 1F shows an illustrative block diagram of the hierarchical controlstructure of the system control software, computer program 70, accordingto a specific embodiment;

FIG. 2 is a simplified vertical cross sectional diagram of a CVDapparatus according to an alternative embodiment of the presentinvention;

FIG. 3 is a flowchart illustrating the formation of a carbon-dopedsilicon oxide layer according to one embodiment of the method of thepresent invention;

FIG. 4 is a graph of substrate temperature versus dielectric constantfor a carbon-doped silicon oxide film deposited in accordance with aparticular embodiment of the present invention;

FIG. 5 is a graph showing the effect of substrate temperature ondeposition rate for a carbon-doped silicon oxide film deposited inaccordance with a particular embodiment of the present invention;

FIGS. 6A-6C are drawings illustrating the gap fill capabilities of filmsdeposited according to the present invention at deposition temperaturesof 150-250° C.;

FIG. 7 is a graph showing the effect of an inert gas flow of helium onfilm uniformity in a carbon-doped silicon oxide film deposited accordingto the present invention;

FIGS. 8A and 8B are graphs of FTIR data that compare the crystallineorientation of a carbon-doped silicon oxide film deposited and curedaccording to the present invention with an uncured film;

FIG. 9 is a flowchart of one process according to the present inventionthat employs a process gas of TMS, ozone and helium;

FIG. 10 is a flowchart illustrating the integration of the formation ofa carbon-doped silicon oxide layer according to an embodiment of themethod of the present invention;

FIG. 11 a is a cross sectional view of an integrated circuit structureundergoing sputtering;

FIG. 11 b is a cross sectional view of an integrated circuit structureundergoing treatment with free atomic hydrogen;

FIG. 12 a depicts a remote RF plasma source according to an embodimentof the present invention;

FIG. 12 b depicts a remote microwave plasma source according to anotherembodiment of the present invention;

FIGS. 13 a-13 e depict FTIR spectra for carbon-doped silicon oxidefilms;

FIGS. 14 a-14 g depict flow diagrams illustrating the integrationenhancements to formation of a carbon-doped silicon oxide layeraccording to another embodiment of the method of the present invention;

FIGS. 15 a-15 h depict a cross section of a partially formed integratedcircuit undergoing integrated processing according to an embodiment ofthe present invention; and

FIGS. 16 a-16 h depict a cross-section of a partially formed integratedcircuit undergoing an integrated dual-damascene process according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

I. Exemplary CVD System

One suitable CVD apparatus in which the method of the present inventioncan be carried out is shown in FIGS. 1A and 1B, which are vertical,cross-sectional views of a CVD system 10, having a vacuum or processingchamber 15 that includes a chamber wall 15 a and chamber lid assembly 15b. Chamber wall 15 a and chamber lid assembly 15 b are shown inexploded, perspective views in FIGS. 1C and 1D.

CVD system 10 contains a gas distribution manifold 11 for dispersingprocess gases to a substrate (not shown) that rests on a heated pedestal12 centered within the process chamber. During processing, the substrate(e.g. a semiconductor wafer) is positioned on a flat (or slightlyconvex) surface 12 a of pedestal 12. The pedestal can be movedcontrollably between a lower loading/off-loading position (depicted inFIG. 1A) and an upper processing position (indicated by dashed line 14in FIG. 1A and shown in FIG. 1B), which is closely adjacent to manifold11. A centerboard (not shown) includes sensors for providing informationon the position of the wafers.

Deposition and carrier gases are introduced into chamber 15 throughperforated holes 13 b (FIG. 1D) of a conventional flat, circular gasdistribution or faceplate 13 a. More specifically, deposition processgases flow into the chamber through the inlet manifold 11 (indicated byarrow 40 in FIG. 1B), through a conventional perforated blocker plate 42and then through holes 13 b in gas distribution faceplate 13 a.

Before reaching the manifold, deposition and carrier gases are inputfrom gas sources 7 through gas supply lines 8 (FIG. 1B) into a mixingsystem 9 where they are combined and then sent to manifold 11.Generally, the supply line for each process gas includes (i) severalsafety shut-off valves (not shown) that can be used to automatically ormanually shut-off the flow of process gas into the chamber, and (ii)mass flow controllers (also not shown) that measure the flow of gasthrough the supply line. When toxic gases are used in the process, theseveral safety shut-off valves are positioned on each gas supply line inconventional configurations.

The deposition process performed in CVD system 10 can be either athermal process or a plasma-enhanced process. In a plasma-enhancedprocess, an RF power supply 44 applies electrical power between the gasdistribution faceplate 13 a and the pedestal so as to excite the processgas mixture to form a plasma within the cylindrical region between thefaceplate 13 a and the pedestal. (This region will be referred to hereinas the “reaction region”). Constituents of the plasma react to deposit adesired film on the surface of the semiconductor wafer supported onpedestal 12. RF power supply 44 is a mixed frequency RF power supplythat typically supplies power at a high RF frequency (RF1) of 13.56 MHzand at a low RF frequency (RF2) of 450 KHz to enhance the decompositionof reactive species introduced into the vacuum chamber 15. In a thermalprocess, RF power supply 44 would not be utilized, and the process gasmixture thermally reacts to deposit the desired films on the surface ofthe semiconductor wafer supported on pedestal 12, which is resistivelyheated to provide thermal energy for the reaction.

During a thermal deposition process, a heat transfer liquid iscirculated through the walls 15 a of the process chamber to maintain thechamber at a constant temperature to prevent condensation of liquidprecursors and reduce gas phase reactions that could create particles. Aportion of these heat-exchanging passages in the lid of chamber 15(passages 18) is shown in FIG. 1B. The passages in the remainder ofchamber walls 15 a are not shown. Fluids used to heat the chamber walls15 a include the typical fluid types, i.e., water-based ethylene glycolor oil-based thermal transfer fluids. This heating (referred to asheating by the “heat exchanger”) beneficially reduces or eliminatescondensation of undesirable reactant products and improves theelimination of volatile products of the process gases and othercontaminants that might contaminate the process if they were to condenseon the walls of cool vacuum passages and migrate back into theprocessing chamber during periods of no gas flow.

The remainder of the gas mixture that is not deposited in a layer,including reaction byproducts, is evacuated from the chamber by a vacuumpump (not shown). Specifically, the gases are exhausted through anannular, slot-shaped orifice 16 surrounding the reaction region and intoan annular exhaust plenum 17. The annular slot 16 and the plenum 17 aredefined by the gap between the top of the chamber's cylindricalside-wall 15 a (including the upper dielectric lining 19 on the wall)and the bottom of the circular chamber lid 20. The 360° circularsymmetry and uniformity of the slot orifice 16 and the plenum 17 helpachieve a uniform flow of process gases over the wafer so as to deposita uniform film on the wafer.

From the exhaust plenum 17, the gases flow underneath a lateralextension portion 21 of the exhaust plenum 17, past a viewing port (notshown), through a downward-extending gas passage 23, past a vacuumshut-off valve 24 (whose body is integrated with the lower chamber wall15 a), and into the exhaust outlet 25 that connects to the externalvacuum pump (not shown) through a foreline (also not shown).

The wafer support platter of the pedestal 12 (preferably aluminum,ceramic, or a combination thereof) is resistively-heated using anembedded single-loop embedded heater element configured to make two fullturns in the form of parallel concentric circles. An outer portion ofthe heater element runs adjacent to a perimeter of the support platter,while an inner portion runs on the path of a concentric circle having asmaller radius. The wiring to the heater element passes through the stemof the pedestal 12. Typically, any or all of the chamber lining, gasinlet manifold faceplate, and various other reactor hardware are madeout of material such as aluminum, anodized aluminum, or ceramic. Anexample of such a CVD apparatus is described in U.S. Pat. No. 5,558,717entitled “CVD Processing Chamber,” issued to Zhao et al. The U.S. Pat.No. 5,558,717 patent is assigned to Applied Materials, Inc., theassignee of the present invention, and is hereby incorporated byreference in its entirety.

A lift mechanism and motor 32 (FIG. 1A) raises and lowers the heaterpedestal assembly 12 and its wafer lift pins 12 b as wafers aretransferred into and out of the body of the chamber by a robot blade(not shown) through an insertion/removal opening 26 in the side of thechamber 15. The motor 32 raises and lowers pedestal 12 between aprocessing position 14 and a lower, wafer-loading position. The motor,valves or flow controllers connected to the supply lines 8, gas deliverysystem, throttle valve, RF power supply 44, and chamber, substrateheating system and heat exchangers H1, H2 are all controlled by a systemcontroller 34 (FIG. 1B) over control lines 36, of which only some areshown. Controller 34 relies on feedback from optical sensors todetermine the position of movable mechanical assemblies such as thethrottle valve and susceptor which are moved by appropriate motors underthe control of controller 34.

In a preferred embodiment, the system controller includes a hard diskdrive (memory 38), a floppy disk drive and a processor 37. The processorcontains a single-board computer (SBC), analog and digital input/outputboards, interface boards and stepper motor controller boards. Variousparts of CVD system 10 conform to the Versa Modular European (VME)standard which defines board, card cage, and connector dimensions andtypes. The VME standard also defines the bus structure as having a16-bit data bus and a 24-bit address bus.

System controller 34 controls all of the activities of the CVD machine.The system controller executes system control software, which is acomputer program stored in a computer-readable medium such as a memory38. Preferably, memory 38 is a hard disk drive, but memory 38 may alsobe other kinds of memory. The computer program includes sets ofinstructions that dictate the timing, mixture of gases, chamberpressure, chamber temperature, RF power levels, susceptor position, andother parameters of a particular process. Other computer programs storedon other memory devices including, for example, a floppy disk or otheranother appropriate drive, may also be used to operate controller 34.

The interface between a user and controller 34 is via a CRT monitor 50 aand light pen 50 b, shown in FIG. 1E, which is a simplified diagram ofthe system monitor and CVD system 10 in a substrate processing system,which may include one or more chambers. In the preferred embodiment twomonitors 50 a are used, one mounted in the clean room wall for theoperators and the other behind the wall for the service technicians. Themonitors 50 a simultaneously display the same information, but only onelight pen 50 b is enabled. A light sensor in the tip of light pen 50 bdetects light emitted by CRT display. To select a particular screen orfunction, the operator touches a designated area of the display screenand pushes the button on the pen 50 b. The touched area changes itshighlighted color, or a new menu or screen is displayed, confirmingcommunication between the light pen and the display screen. Otherdevices, such as a keyboard, mouse, or other pointing or communicationdevice, may be used instead of or in addition to light pen 50 b to allowthe user to communicate with controller 34.

The process for depositing the film can be implemented using a computerprogram product that is executed by controller 34. The computer programcode can be written in any conventional computer readable programminglanguage: for example, 68000 assembly language, C, C++, Pascal, Fortranor others. Suitable program code is entered into a single file, ormultiple files, using a conventional text editor, and stored or embodiedin a computer usable medium, such as a memory system of the computer. Ifthe entered code text is in a high level language, the code is compiled,and the resultant compiler code is then linked with an object code ofprecompiled Windows™ library routines. To execute the linked, compiledobject code the system user invokes the object code, causing thecomputer system to load the code in memory. The CPU then reads andexecutes the code to perform the tasks identified in the program.

FIG. 1F is an illustrative block diagram of the hierarchical controlstructure of the system control software, computer program 70, accordingto a specific embodiment. Using the light pen interface, a user enters aprocess set number and process chamber number into a process selectorsubroutine 73 in response to menus or screens displayed on the CRTmonitor. The process sets are predetermined sets of process parametersnecessary to carry out specified processes, and are identified bypredefined set numbers. The process selector subroutine 73 identifies(i) the desired process chamber and (ii) the desired set of processparameters needed to operate the process chamber for performing thedesired process. The process parameters for performing a specificprocess relate to process conditions such as, for example, process gascomposition and flow rates, temperature, pressure, plasma conditionssuch as RF power levels and the low frequency RF frequency, cooling gaspressure, and chamber wall temperature. These parameters are provided tothe user in the form of a recipe, and are entered utilizing the lightpen/CRT monitor interface.

The signals for monitoring the process are provided by the analog anddigital input boards of the system controller, and the signals forcontrolling the process are output on the analog and digital outputboards of CVD system 10.

A process sequencer subroutine 75 comprises program code for acceptingthe identified process chamber and set of process parameters from theprocess selector subroutine 73, and for controlling operation of thevarious process chambers. Multiple users can enter process set numbersand process chamber numbers, or a user can enter multiple process setnumbers and process chamber numbers, so the sequencer subroutine 75operates to schedule the selected processes in the desired sequence.Preferably, the sequencer subroutine 75 includes a program code toperform the steps of (i) monitoring the operation of the processchambers to determine if the chambers are being used, (ii) determiningwhat processes are being carried out in the chambers being used, and(iii) executing the desired process based on availability of a processchamber and type of process to be carried out. Conventional methods ofmonitoring the process chambers can be used, such as polling. Whenscheduling which process is to be executed, sequencer subroutine 75takes into consideration the present condition of the process chamberbeing used in comparison with the desired process conditions for aselected process, or the “age” of each particular user entered request,or any other relevant factor a system programmer desires to include fordetermining scheduling priorities.

Once the sequencer subroutine 75 determines which process chamber andprocess set combination is going to be executed next, the sequencersubroutine 75 initiates execution of the process set by passing theparticular process set parameters to a chamber manager subroutine 77a-c, which controls multiple processing tasks in a process chamber 15according to the process set determined by the sequencer subroutine 75.For example, the chamber manager subroutine 77 a comprises program codefor controlling sputtering and CVD process operations in the processchamber 15. The chamber manager subroutine 77 also controls execution ofvarious chamber component subroutines that control operation of thechamber components necessary to carry out the selected process set.Examples of chamber component subroutines are substrate positioningsubroutine 80, process gas control subroutine 83, pressure controlsubroutine 85, heater control subroutine 87, and plasma controlsubroutine 90. Those having ordinary skill in the art will readilyrecognize that other chamber control subroutines can be includeddepending on what processes are to be performed in the process chamber15. In operation, the chamber manager subroutine 77 a selectivelyschedules or calls the process component subroutines in accordance withthe particular process set being executed. The chamber managersubroutine 77 a schedules the process component subroutines much likethe sequencer subroutine 75 schedules which process chamber 15 andprocess set are to be executed next. Typically, the chamber managersubroutine 77 a includes steps of monitoring the various chambercomponents, determining which components need to be operated based onthe process parameters for the process set to be executed, and causingexecution of a chamber component subroutine responsive to the monitoringand determining steps.

Operation of particular chamber component subroutines will now bedescribed with reference to FIG. 1F. The substrate positioningsubroutine 80 comprises program code for controlling chamber componentsthat are used to load the substrate onto pedestal 12 and, optionally, tolift the substrate to a desired height in the chamber 15 to control thespacing between the substrate and the gas distribution manifold 11. Whena substrate is loaded into the process chamber 15, pedestal 12 islowered to receive the substrate, and thereafter, the susceptor 12 israised to the desired height in the chamber, to maintain the substrateat a first distance or spacing from the gas distribution manifold duringthe CVD process. In operation, the substrate positioning subroutine 80controls movement of pedestal 12 in response to process set parametersrelated to the support height that are transferred from the chambermanager subroutine 77 a.

The process gas control subroutine 83 has program code for controllingprocess gas composition and flow rates. The process gas controlsubroutine 83 controls the open/close position of the safety shut-offvalves, and also ramps up/down the mass flow controllers to obtain thedesired gas flow rate. The process gas control subroutine 83 is invokedby the chamber manager subroutine 77 a, as are all chamber componentsubroutines, and receives from the chamber manager subroutine processparameters related to the desired gas flow rates. Typically, the processgas control subroutine 83 operates by opening the gas supply lines andrepeatedly (i) reading the necessary mass flow controllers, (ii)comparing the readings to the desired flow rates received from thechamber manager subroutine 77 a, and (iii) adjusting the flow rates ofthe gas supply lines as necessary. Furthermore, the process gas controlsubroutine 83 includes steps for monitoring the gas flow rates forunsafe rates and for activating the safety shut-off valves when anunsafe condition is detected.

In some processes, an inert gas such as helium or argon is flowed intothe chamber 15 to stabilize the pressure in the chamber before reactiveprocess gases are introduced. For these processes, the process gascontrol subroutine 83 is programmed to include steps for flowing theinert gas into the chamber 15 for an amount of time necessary tostabilize the pressure in the chamber, and dilute the reactant so thatthere is a uniform reaction. Then the steps described above would becarried out. Additionally, when a process gas is to be vaporized from aliquid precursor, for example, tetraethylorthosilane (“TEOS”), theprocess gas control subroutine 83 is written to include steps forbubbling a delivery gas, such as helium, through the liquid precursor ina bubbler assembly or introducing a carrier gas, such as helium ornitrogen, to a liquid injection system.

The pressure control subroutine 85 comprises program code forcontrolling the pressure in the chamber 15 by regulating the size of theopening of the throttle valve in the exhaust system of the chamber. Thesize of the opening of the throttle valve is set to control the chamberpressure to the desired level in relation to the total process gas flow,size of the process chamber, and pumping setpoint pressure for theexhaust system. When the pressure control subroutine 85 is invoked, thedesired, or target, pressure level is received as a parameter from thechamber manager subroutine 77 a. The pressure control subroutine 85operates to measure the pressure in the chamber 15 by reading one ormore conventional pressure manometers connected to the chamber, tocompare the measure value(s) to the target pressure, to obtain PID(proportional, integral, and differential) values from a stored pressuretable corresponding to the target pressure, and to adjust the throttlevalve according to the PID values obtained from the pressure table.Alternatively, the pressure control subroutine 85 can be written to openor close the throttle valve to a particular opening size to regulate thechamber 15 to the desired pressure.

The heater control subroutine 87 comprises program code for controllingthe current to a heating unit that is used to heat the substrate 20and/or the heat exchanger. The heater control subroutine 87 is alsoinvoked by the chamber manager subroutine 77 a and receives a target, orset-point, temperature parameter. The heater control subroutine 87measures the temperature by measuring voltage output of a thermocouplelocated in pedestal 12 chamber 15, or lid assembly 15 a, comparing themeasured temperature to the set-point temperature, and increasing ordecreasing current applied to the heating unit to obtain the set-pointtemperature. The temperature is obtained from the measured voltage bylooking up the corresponding temperature in a stored conversion table,or by calculating the temperature using a fourth-order polynomial. When,for example, an embedded loop is used to heat pedestal 12, the heatercontrol subroutine 87 gradually controls a ramp up/down of currentapplied to the loop. Additionally, a built-in fail-safe mode can beincluded to detect process safety compliance, and can shut downoperation of the heating unit if the process chamber 15 is not properlyset up.

The plasma control subroutine 90 comprises program code for setting thelow and high frequency RF power levels applied to the process electrodesin the chamber 15 and for setting the low frequency RF frequencyemployed. Similar to the previously described chamber componentsubroutines, the plasma control subroutine 90 is invoked by the chambermanager subroutine 77 a.

The above reactor description is mainly for illustrative purposes, andother thermal CVD equipment such as the Giga-fill chamber manufacturedby Applied Materials may be employed. Additionally, variations of theabove-described system, such as variations in pedestal design, heaterdesign, RF power frequencies, location of RF power connections andothers are possible. For example, the wafer could be supported by asusceptor and heated by quartz lamps. The method of the presentinvention is not limited to any specific CVD apparatus.

II. Exemplary Deposition of an IMD Layer

Certain embodiments of the present invention relate to deposition of acarbon-doped silicon oxide low k film using a thermal CVD process. Otherembodiments of the present invention enhance the adhesion and stabilityof thin films including carbon-doped silicon oxide films deposited froman ozone/organosilane precursor gas according the method discovered bythe present inventors. Embodiments of the invention can be practiced ina CVD deposition chamber such as the exemplary chamber described above.Embodiments of the present invention related to the deposition of a lowk thermal CVD carbon-doped silicon oxide film are particularly usefulfor the deposition of premetal and intermetal dielectric layers(sometimes referred to as interlevel dielectric layers), especiallythose used for sub-0.2 micron applications.

FIG. 3 is a flowchart illustrating the formation of a carbon-dopedsilicon oxide layer according to one embodiment of the presentinvention. As shown in FIG. 3, the film is deposited by flowing anorganosilane precursor gas and ozone into a substrate processing chamberand heating the substrate within the chamber to a temperature less thanabout 250° C. (step 305). The deposition process is a thermal, asopposed to plasma, CVD process. After the film is deposited, it is thencured (step 310) to form a stable polymeric structure and increase itsresistance to moisture absorption. In order to form a film having asufficiently low dielectric constant, it is important that theorganosilane precursor gas used for film deposition have at least onesilicon-carbon bond. Examples of such precursor gases includemethylsilane, dimethylsilane (DMS), trimethylsilane (TMS),tetramethylsilane (T4MS) and phenylmethylsilane among others. Because oftheir commercial availability and high number of silicon-carbon bonds,TMS and T4MS are the currently most preferred precursor gases. Furtherdetails of the preferred deposition process conditions and preferredcuring processes are discussed in detail below.

The present inventors have found that the dielectric constant ofcarbon-doped silicon oxide film deposited in step 305 is directlyrelated to the temperature of the substrate during deposition. In orderto deposit a film having a dielectric constant that is sufficient forlow k applications (e.g., a k less than or equal to 3.0), it isimportant that the deposition temperature be kept below 250° C.Temperatures lower than 250° C. are preferred in other embodiments.

As used herein “deposition temperature” refers to the temperature of thesubstrate during deposition. In the currently preferred embodiments, thesubstrate is directly heated by the pedestal heater. At higherpressures, e.g., 200 Torr and above, the substrate temperature ispractically equal to the pedestal temperature (substrate temperature maybe about 10° C. less) due to conduction and convection heating. At nearvacuum pressures, however, (e.g., less than 50 Torr) there may be a50-60° C. temperature difference between the substrate and pedestalbecause of the lack of convection heating. Thus, at these lower pressurelevels, the pedestal temperature can be set up to 50-60° C. higher thanthe desired deposition temperature.

FIG. 4 is a graph showing the effect of temperature on dielectricconstant for a particular set of deposition conditions at a depositionpressure above 200 Torr. As shown in FIG. 4, a pedestal temperature of250° C. resulted in a dielectric constant of 4.6 while pedestaltemperatures of 200° C. and 150° C. resulted in dielectric constants of3.0 and 2.7 respectively. Thus, as evident from the figure and fromother tests the inventors ran, a temperature of 200° C. and below ispreferred. It is believed that the deposition temperature has a directeffect on the amount of carbon incorporated into the deposited film.Silicon oxide films having higher carbon concentration levels generallyhave a lower dielectric constant than silicon oxide films having lowercarbon levels, other dopant concentrations being similar. Filmsdeposited according to the present invention preferably have a carboncontent of at least 8 atomic percent and more preferably at least 10atomic percent.

Deposition temperature is also important, however, in achieving gasphase reactions between ozone and the organosilane precursor. Ozoneactivates through these gas phase collisions and a sufficiently hightemperature is required to ensure a commercially acceptable depositionrate. Thus, while it is important to have a sufficiently low depositiontemperature to obtain an appropriate low dielectric constant, this mustbe balanced against deposition rate. FIG. 5 is a graph showing theeffect of pedestal temperature on deposition rate. For FIG. 5 acarbon-doped silicon oxide film was deposited at a pressure of 200 Torrand spaced 250 mils from the gas distribution manifold. A process gas ofTMS (170 sccm), 12.5 wt. % ozone (1000 sccm and helium (6000 sccm) wasflowed into the chamber and the pedestal temperature was varied from150° C. to 350° C. As shown in FIG. 5, deposition rate increases as thepedestal temperature is increased. The activation energy of thereaction, however, is only 3.8 kcal/mol, indicating that the reactioncontrolling step is in the gas phase. In order to achieve a commerciallyacceptable deposition rate for IMD and PMD applications, it is useful tomaintain the pedestal temperature at about 100° C. or above. In anotherset of experiments and tests, the deposition rate of carbon-dopedsilicon oxide films was measured for pedestal temperature of 100° C.,150° C. and 200° C. In these tests, the 200° C. process had a depositionrate of about 1000 Å/min and the 150° C. process had a rate of about 500Å/min. Below 100° C., however, the process had a deposition rate ofabout 50 Å/min—a rate that is currently considered too low for practicalcommercial applications as an IMD or PMD layer. At depositiontemperatures sufficiently below 100° C. ozone may not be activated anddeposition may not occur at all.

A technique the inventors have devised to increase the deposition rateat a given pedestal temperature concerns heating at least the upperportion of the substrate processing chamber with the heat exchanger (thetemperature controlled liquid that circulates through passages in thechambers walls described in the exemplary chamber section). In mostconventional TEOS/ozone IMD deposition applications, the substrate isheated to a temperature of at least 400° C. In a cold wall reactor thisheating is done primarily by heating the substrate directly (i.e., witha heated pedestal). At such a relatively high deposition temperature,the effect of the heat exchanger on the deposition process is minimal.That is, the heat exchanger cannot alter process conditions in anysignificant manner to be thought of as an additional “control knob” forthe process.

The present inventors, however, have determined that because of therelatively low substrate temperatures that are preferred for the presentinvention, the heat exchanger can have a significant effect ondeposition rate. Specifically, the heat exchanger can be used as anadditional “control knob” to increase the deposition rate of thecarbon-doped silicon oxide film. The inventors have determined thatheating the glycol/water mixture to a temperature above the normallyrecommended temperature of 65° C. helps activate ozone in the gas phase,which in turn leads to an increased deposition rate for the growingfilm, a lower dielectric constant and better gap fill properties. Otherembodiments of the invention, use the heat exchanger to heat theglycol/water mixture to between 55 and 100° C.

In previously known systems only a single heat exchanger and heatexchange loop was coupled to passages 18 a and passages 18 b. Therefore,the walls 15 a and lid 15 b were kept at approximately the sametemperature. Since the temperature was chosen to optimize the depositionreaction in the chamber 15, organosilane precursor tended to reactbehind the blocker plate 42 in such a way as to choke off the flow ofgas through the gas distribution manifold 11. To, overcome this, thedeposition chamber can be configured to provide separate control of thetemperature of the chamber walls and the temperature of the chamber lidassembly. In one embodiment, depicted in FIG. 2, chamber 15 is equippedwith two heat exchangers H1 and H2 coupled to separate heat exchangeloops L1 and L2 respectively. Heat exchangers H1 and H2 mechanisms fortransfer of thermal energy to or from heat transfer medium, such asfluids circulating in heat exchange loops L1 and L2. Such thermal energytransfer can heat the fluid, e.g., resistively, conductively,convectively, radiatively or by exothermic chemical reaction.Alternatively, such thermal energy transfer can cool the fluid, e.g.,conductively, convectively, radiatively, evaporatively, by Peltiereffect or by endothermic chemical reaction.

Heat exchange loop L1 is coupled to passages 18 a in the walls 15 a ofchamber 15. Heat exchange loop L2 is coupled to passages 18 b in lidassembly 15 b, e.g., in gas distribution manifold 11. Loop L1 and L2 arenot fluidly coupled to each other. Thus it is possible, for example toheat walls 15 a while cooling lid assembly 15 b. This is useful when,for example, it is desired to optimize the reaction occurring withinchamber 15, while at the same time inhibiting reaction of reactants ingas distribution manifold, e.g., behind blocker plate 42. A specificexample of a suitable heat exchanger H1 is an AMAT-0 unit, manufacturedby Applied Materials of Santa Clara. Such a heat exchanger unit isgenerally capable of maintaining the chamber walls 15 a at between 45and 100° C. A specific example of heat exchanger H2 is a refrigeratedbath unit model AMAT RTE-140, manufactured by NESLAB of Portsmouth, N.H.Such a unit is generally capable of maintaining the 15 b at atemperature of between −40 and 100° C. Both units use a 50-50 mixture ofglycol and water as a heat transfer medium.

In one embodiment, heater control subroutine maintains the chamber walls15 a at a temperature of approximately 60° C. and lid assembly 15 b at atemperature of approximately 25° C. during deposition of a low-kmaterial with an organosilane precursor. Operating the system in thismanner inhibits thermal reaction of the precursor behind the blockerplate 42 and prevents choking of the flow of gas through the gasdistribution manifold 11. Consequently, the deposition rate can besubstantially increased compared to deposition performed with a singleheat exchanger coupled to both lid assembly 15 b and walls 15 a. Heatercontrol subroutine 87 can be configured to separately control heatexchangers H1 and H2.

The inventors have also determined that the gap fill properties of thecarbon-doped silicon oxide film deposited according to the presentinvention are better at lower substrate deposition temperatures ascompared with higher deposition temperatures. FIGS. 6A-6C are sketchesshowing the cross-sectional view of a film deposited according to thepresent invention over adjacent raised surfaces. FIG. 6A shows a filmdeposited at a pedestal temperature of 250° C., while the film in FIG.6B was deposited at 200° C. and the film in FIG. 6C was deposited at150° C. As shown in the figures, the gap fill capability of the 150° C.film is significantly better than the higher temperature films. Higherwall temperatures, however, improve the gap fill properties of the film.Specifically, in a dual heat exchange systems higher settings of heatexchange H1 operatively coupled to the walls encircling the substrateraise the wall temperatures. It is believed that these improvedproperties are due to the effect the heat exchanger has on ozoneactivation in the gas phase. Increasing the wall temperature leads to anincrease in the gas phase temperature as well as an increase in ozonedecomposition in the gas phase reaction.

While the overall deposition pressure can be varied between 1-760 Torrto help obtain desired film properties, it is important that the partialpressure of the organosilane precursor be kept below its vapor pressurein the deposition environment. The formula for partial pressure of theorganosilane precursor is set forth as formula (1) below:(Organosilane Flow/Total Gas Flow)×Chamber Pressure  (1)

As evident from the above equation, the flow rate of the organosilanegas is limited by its partial pressure. The flow rate of theorganosilane gas has a direct effect on the film deposition rate. It isgenerally desirable to introduce as much of the organosilane as possiblein order to ensure a sufficiently high deposition rate. As would beknown to those of skill in the art, the chemical supplier, e.g., acompany such as Dow Corning, can provide a list of recommended maximumgas flows at various pressures for organosilane precursors (e.g., TMS)that they supply.

In some embodiments it is preferred that deposition pressure be setabove about 50 Torr and below about 450 Torr. Higher pressures generallyincrease the gas phase reactions of the ozone/organosilane reaction. Itis desirable that the gas phase reactions result in a final product(carbon-doped silicon oxide) being formed on the surface of thesubstrate. If the gas phase reaction is too strong (e.g., at a pressurelevel about 450 Torr), final product may be formed in the gas phaseabove the substrate surfaces rather than on the surface. Pressures above50 Torr are generally desirable to promote good heat transfer betweenthe substrate and pedestal and to achieve good gap fill performancecharacteristics.

The ozone flow rate also has a strong effect on deposition rate. Flowingmore ozone into the chamber allows for more gas phase reactions betweenthe ozone and the organosilane thereby increasing the rate of filmdeposition. Similarly, flowing a higher concentration of ozone, forexample, 16 wt. % as opposed to 8 wt. %, also results in an increase inthe deposition rate.

Preferred embodiments of the present invention also introduce an inertgas flow, in addition to the organosilane and ozone precursor gas flows,into the chamber during the deposition process. The inert gas flow helpsstabilize the deposition process and improves the thickness uniformityof the deposited film. Currently preferred embodiments introduce a flowof helium as the inert gas, but other embodiments can introduce othergases such as argon or nitrogen. The inert gas should not includeelements that incorporate into the film in any significant manner.

FIG. 7 is a graph showing the effect of an inert gas flow of helium onfilm uniformity. As evident by FIG. 7, the inventors have determinedthat a high flow of helium improves film uniformity, but once the flowreaches a certain rate, 6000 sccm for this particular set of depositionconditions, a further increase in the inert gas flow does not furtherimprove film uniformity. The addition of a high flow of helium does notadversely affect other film qualities such as deposition rate orrefractive index.

Higher deposition pressure levels generally result in better gap fillproperties but lower deposition rate and dielectric constants. Thus, itis important to balance these resulting characteristics depending on thedesired physical properties of the deposited film. In one set ofexperiments, in which the pedestal temperature was set to 200° C., theheat temperature of a single exchanger coupled to both the lid and wallswas set to 55° C., spacing was set to 210 mils and a process gas of TMS(170 sccm), helium (6000 sccm) and 12.5 wt. % ozone (4000 sccm) wasintroduced, pressure was set to 50 Torr and then to 200 Torr. At 50 Torrthe film had a deposition rate of 978 Å/min and a k of 2.58. At 200 Torrthe film had a deposition rate of 831 Å/min and a k of 2.69. The gapfill properties of the 200 Torr film were improved as compared to the 50Torr film, however.

One experiment was performed in a chamber wherein separate heatexchangers were configured to maintain the walls at approximately 55° C.and the lid assembly at about 25° C. The other deposition conditionswere approximately the same as in the previous example, however the filmhad a deposition rate of approximately 1700 Å/min at a pressure of 100torr.

The present inventors have found that, subsequent to film deposition, afilm cure step (FIG. 3, step 310) can improve film stability, especiallyif the deposited film is subject to an environment, e.g., the clean roomambient, that contains moisture. Such a cure process forces out moisturealready absorbed into the film and changes the film structure so that itis more moisture resistant. The cure process removes undesirable Si—O“cage like” bonds and replaces them with the more desirable Si—O“network” type bonds as would be understood by a person of skill in theart.

FIGS. 8A and 8B compare a cured carbon-doped silicon oxide film withuncured film. FIG. 8A shows Fourier transform infrared spectrometry(FTIR) data of an as deposited carbon-doped silicon oxide film depositedfrom TMS, ozone and helium precursor gas mixture. As shown in FIG. 8A,the film contains a relatively high number of Si—O cage-like bonds(wavenumber 1150 cm⁻¹) and very few of the desirable Si—O network typebonds. The cage-like bonds have dangling bonds and are susceptible toattracting hydrogen atoms in the presence of moisture such as moisturevapor. As shown in FIG. 8B, once the film is cured, however, many of theSi—O cage-like bonds are converted to the network type bonds resultingin a more stable, highly moisture resistant film. The film deposited forthe test shown in FIG. 8A also exhibited a strong stress hysteresis whenheated and subsequently cooled and a high dielectric constant (k=5.5)due to moisture absorption when exposed to the ambient for a one weekperiod. In contrast, the film deposited and cured for the test in FIG.8B, exhibited no stress hysteresis when heated and subsequently cooledand retained a low dielectric constant (k=2.5) even when exposed to theambient for a week.

Several different processes can be performed to effectively cure filmsdeposited according to the present invention. Two process that shouldnot be used, however, include an oxygen plasma cure or a cure in anozone rich furnace environment. Such processes can result in oxygenatoms reacting with the deposited film and removing the highly desirableSi—C bonds. When this happens the dielectric constant of the filmgreatly increases and the film becomes unsuitable for applicationsrequiring low dielectric constants.

Instead, the cure process can be performed in a conventional furnacewith a relatively inert atmosphere, e.g., nitrogen, oxygen, or ammonia,or under vacuum conditions. In either case, the cure can be done insitu, i.e., without breaking vacuum, or ex situ, but ex situ processesare generally preferred since in situ processes require use of arelatively expensive deposition chamber and can significantly reducethroughput of the tool.

In either a conventional furnace or vacuum chamber, the cure processheats the film to a temperature between about 300-500° C. for at leastabout 10 minutes. Higher temperature cures generally take less time thanlower temperature ones. For example, a 300° C. cure may last for 40-60minutes while a 500° C. cure may last for 10-20 minutes.

In a specific embodiment, a vacuum cure heats the substrate to atemperature of about 400° C. for a period of about 10 minutes in a lowpressure nitrogen environment. Such a process stabilizes the depositedfilm so that it resists moisture absorption in the future. The substratemay be transferred to another chamber, e.g. a different chamber in thesame cluster tool as the deposition chamber, for curing without breakingvacuum. A specific embodiment of a conventional furnace cure also heatsthe substrate to a temperature of about 400° C. for a period of about 30minutes in a nitrogen atmosphere.

Instead of placing the substrate in a vacuum environment, however, thesubstrate is placed in a molecular nitrogen (N₂) environment atatmospheric pressure. The furnace cure process is preferred to a vacuumcure in some embodiments because it achieves similar or even better filmresults with less expensive equipment and increased throughput.Throughput is increased because wafers can be transferred into and outof the furnace, which can heat multiple wafers at a time, one at a timeas they have finished the curing cycle, e.g., 30 minutes. While a vacuumchamber can also heat and cure multiple wafers at a time, the wafers areloaded and unloaded in batches so as to not break vacuum while thecuring process is underway.

FIG. 9 is a flowchart of one embodiment of a thermal deposition process,shown in FIG. 3 as step 305, that employs a process gas of TMS, ozoneand helium. The process set forth in FIG. 9 is for exemplary purposesonly and should not be considered limiting to the scope of the presentclaims. The deposition process is initiated, after a wafer has beenloaded into the deposition chamber, by flowing helium (6000 sccm) andoxygen (4000 sccm) gases while keeping the throttle valve fully open(step 400) for several seconds in order to stabilize the gas flows.Oxygen (O₂) is added to the helium flow at the same rate at which ozoneis subsequently added. Flowing oxygen in this manner results in asubstantially constant oxygen/helium ratio throughout the depositionprocess. It is believed that maintaining such a constant ratio improvesfilm uniformity. An ozone flow is not introduced at this stage becausethe high reactivity of ozone.

Once the gas flow has stabilized, the throttle valve is partially closedand the pressure within the chamber is brought to the desired depositionpressure level in the presence of the helium and oxygen flows (step405). Once the desired pressure level is reached and maintained for acouple of seconds, an ozone flow (4000 sccm) is substituted for theoxygen flow and a flow of TMS is initiated (500 sccm) to deposit acarbon-doped silicon oxide film (step 410). Deposition step 410 ismaintained until the carbon-doped silicon oxide layer reaches a desiredthickness and then the ozone flow is shut off (step 415). The ozone flowis switched off prior to the TMS flow in order to allow the TMS to reactwith residual ozone in the gas phase. The present inventors havedetermined that shutting off the ozone and TMS flows simultaneously canresult in ozone reacting with carbon in the deposited film. The TMS flowis then shut off several seconds after the ozone flow (step 420) and thedeposition pressure is released by opening the throttle valve whilemaintaining the helium flow (step 425). Finally, all the gases are shutoff (step 430).

The pedestal and heat exchanger temperatures are set and stabilizedprior to film deposition. All three temperatures are maintainedapproximately constant throughout deposition. In the above example, boththe walls and lid of the deposition chamber were maintained at atemperature of about 55° C. Generally these temperatures are set andremain unchanged throughout an entire run of multiple wafer depositions.

In an alternative embodiment, the chamber walls are maintained at atemperature of about 60° C. and lid assembly is maintained at about 25°C. In this embodiment the helium flow rate is 8000 sccm and the oxygenflow rate is 5000 sccm in step 400.

As described above, the present invention deposits a carbon-dopedsilicon oxide film that has good gap fill capabilities and a lowdielectric constant. The film is also highly conformal. Films depositedaccording to the present invention are porous when compared to thermalsilicon oxide. For example, thermal silicon oxide films generally have adensity of between 2.1-2.2 g/cm³. Films deposited according to thepresent invention, however, generally have a density of less than orequal to about 1.2 g/cm³.

The porosity of the film is provided by very small or micropores asopposed to larger pores found in some porous oxide films. Generally,these micropores are evenly distributed throughout the film and havediameters less than about 100 Å. The present inventors have demonstratedthat films deposited according to the present invention exhibit uniformremoval rates across the surface of an entire wafer when subject to aCMP step. This is especially important for damascene processes that areused for the fabrication of many integrated circuits today as thesurface of the film can become highly planarized after the CMP stepallowing for very fine patters to be focused on a subsequently depositedmetal layer film during a photolithography step. In one series of tests,films deposited according to the present invention exhibited CMP removalrates of 3687 Å/min. and 3087 Å/min. at a nonuniformity rate of 4 and 5percent, respectively, as measured at 49 points across the surface ofthe wafer as would be understood by a person of ordinary skill in theart. These test results compared favorably to removal of a thermal oxidefilm at a rate of 1100 Å/min at a nonuniformity rate of 3 percent.

The gas flow rates recited and described above are optimized fordeposition processes run in a Gigafill or DxZ chamber manufactured byApplied Materials and outfitted for 200 mm wafers. A person of ordinaryskill in the art will recognize that the rates at which variousprecursor gases in the process gas are introduced are in part chamberspecific and will vary if chambers of other design and/or volume areemployed.

In other embodiments of the present invention, one or more dopants mayoptionally be included with the organosilane and ozone during depositionof the low-k layer for both PMD and IMD applications. For examplephosphorous (P) may be added using, e.g., phosphine (PH₃) during thedeposition described above to getter alkali metals, e.g., sodium (Na),thereby reducing metal contamination of the deposited film. Boron may beadded, e.g. using diborane (B₂H₆). Boron tends to make the depositedfilm flow easily but also diffuses easily. Diffusion of Boron from theSi—O—C layer into an underlying silicon substrate might be useful fordoping the silicon for making a device, such as a gate structure.Alternatively, both boron (B) and phosphorous may be added duringdeposition to produce a film that has a reduced viscosity and can bereflowed to achieve high aspect ratio gap-fill for PMD applications.

The inventors of the present invention have also discovered that thedeposition rate and gap fill properties of Si—O—C films are optimizedunder different conditions. For example, the deposition rate of Si—O—Cfilms is optimized when deposited with organosilanes at low pressure,i.e., about 150 torr or less and high temperature, i.e., greater thanabout 150° C. Gap fill properties of Si—O—C films, e.g., step coverage,are optimized when the film is deposited at relatively high pressure,i.e., greater than about 200 torr, and low temperature, i.e., about 125°C. or less. The conditions that optimize gap fill generally produce lowdeposition rates. The conditions that optimize deposition rate generallyprovide poor gap-fill. Since the conditions that optimize depositionrate and gap fill are contradictory to each other, it is problematic tooptimize both in a single step deposition process.

To overcome this, an alternative embodiment of the deposition methoddescribed above optimizes both gap fill and deposition rate by dividingthe deposition into two steps. The first step is optimized for gap fillwhile the second step is optimized for deposition rate. The first andsecond steps are performed with the gas mixtures and flow ratesessentially as set forth above with respect to FIG. 9. In the firststep, the throttle valve position is set to establish a pressure ofbetween 200 and 700 torr, preferably about 200 torr while the pedestalis maintained at a temperature of about 125° C. In the second stephelium is provided at 8000 sccm and 15% by weight of O₃ in O₂ isprovided at 5000 sccm. The pedestal temperature is raised to betweenabout 150 and 170° C. while the pressure is maintained at between 50 and150 torr, preferably about 100 torr.

In another version of this embodiment, the second step can be a PECVDprocess. For example, a Si—O—C type low-k film can be deposited byenergizing a process gas mixture of an organosilane with nitrous oxide(N₂O) or O₂ to form a deposition plasma. Suitable organosilanes includemethylsilane, dimethylsilane (DMS), trimethylsilane (TMS),tetramethylsilane (T4MS) and phenylmethylsilane among others. The PECVDSi—O—C layer is under a compressive stress. The thermal deposited Si—O—Clayer is under tensile stress. When the two layers are deposited on topof one another to form a combined film the compressive and tensilestresses tend to compensate for each other producing a low stress film.Such a low stress film would be resistant to cracking.

III. Process Integration of Deposition of a Low Dielectric ConstantLayer

While the above described ozone/organosilane carbon-doped silicon oxidefilm is useful for a variety of applications, the present inventors havedeveloped a number of pre-deposition and post-deposition steps thatfacilitate the integration of a low k ozone/organosilane carbon-dopedsilicon oxide film according to the present invention into establishedintegrated circuit manufacturing processes. One example of such amultistep process is depicted in FIG. 10. As shown in FIG. 10, theprocess starts with a pre-deposition treatment 1000 to enhance theadhesion of the film to underlying aluminum. The pre-depositiontreatment 1000 uses free atomic hydrogen to reduce an aluminum oxidethat builds up on the aluminum. In a specific embodiment, free atomichydrogen is dissociated from a hydrogen-containing gas in a remotesource. In another specific embodiment, the remote source energizes thehydrogen containing gas with electromagnetic radiation. In a preferredembodiment the electromagnetic radiation is in the form of microwaves.Further details of predisposition step 1000 are described below inconjunction with FIGS. 11 a and 11 b.

After pretreatment step 1000, layer of carbon-doped silicon oxide isdeposited in step 1010 using an organosilane and ozone. This step haselements in common with the method set forth above with respect to FIG.3 and FIG. 9.

An optional post deposition treatment 1020 further enhances adhesion byreducing shrinkage of the deposited film. This step is generallyperformed if the film is to be cured ex-situ. The post-depositiontreatment 1020 takes place in a reducing environment. In a preferredembodiment, the deposited film is treated in a reducing environment ofammonia for approximately one minute at a temperature of approximately400° C.

The method then proceeds to a cure 1030 (step 310 from FIG. 3), whichmay be performed either in-situ or ex-situ. After cure 1030, the filmcan be densified at 1040 to reduce outgassing of a subsequentlydeposited cap layer. In a preferred embodiment, the cured film isdensified in a nitrogen-containing plasma. After densification 1040, thefilm can be capped at 1050 to prevent cracking of the film. In oneembodiment, a cap layer of silicon oxide is deposited over the densifiedfilm by plasma enhanced chemical vapor deposition (PECVD). Furtherdetails of steps 1020, 1040 and 1050 are set forth in Section V, VI andVII below.

IV. Pre-Deposition Treatment

Predeposition step 1000 discussed in FIG. 10 provides for strongadhesion of a layer of material deposited on an underlying substrate.For example, in some IMD applications a dielectric layer, such as aTMS-ozone layer, may adhere poorly to an underlying metal. Postdeposition heating processes, such as cure processes, may cause thedeposited film to shrink. As a result of the shrinkage, the depositedlayer can become delaminated from the underlying metal. The adhesionproblem is illustrated in FIG. 11 a, which depicts a partially formedintegrated circuit 1100. Integrated circuit 1100 generally includes anoxide layer 1102 and metal lines 1104 separated by a gap 1106. An uppersurface 1105 of metal lines 1104 may be coated with a thin barrier suchas titanium nitride (TiN). In the case of aluminum metal lines 1104,poor adhesion is believed to the result of a thin layer 1110 of aluminumoxide (Al_(x)O_(y)) on the surface of vertical walls 1112 of metal lines1104. If oxide forming layer 1110 is one that forms readily at roomtemperature, layer 1110 tends to be weakly bonded to the underlyingmetal, i.e. metal lines 1104. Consequently a film deposited over oxide1110 may become delaminated from metal lines 1104.

Previously known methods used to remove such an oxide layer includesputtering in a plasma. Ions from the plasma are accelerated towards thecircuit 1100 in the direction shown by arrows 1114 by an electric field.Sputtering is effective at removing oxide from a bottom of gap 1106.Unfortunately because of the direction of acceleration of the ions, theplasma is much less effective at removing the oxide from the walls 1112.

To overcome this, one embodiment of the present invention includes apre-treatment step in which the oxide layer is reduced with free atomichydrogen. The pre-treatment is illustrated in FIG. 11 b. Free atomichydrogen 1120 attacks the oxide in a purely thermal reaction in alldirections as shown by arrows 1122. Since the thermal reaction isnon-directional hydrogen 1122 can attack oxide 1110 on vertical walls1112. Such a pretreatment can effectively remove aluminum oxide and mayalso be effective in reducing other metal oxides such as copper oxides(Cu_(x)O_(y)). Furthermore, such a pre-treatment is generallyadvantageous when a surface of a substrate contains a weakly bound oxidethat would impair adhesion of a subsequently deposited layer ofmaterial.

As shown in FIG. 2, a remote source, fluidly coupled to the processchamber provides free atomic hydrogen for the pre-treatment. The remotesource supplies energy that dissociates a hydrogen-containing gas suchas ammonia (NH₃) or molecular hydrogen (H₂). Such a remote source can bea purely thermal source, in which hydrogen containing gas is dissociatedby heating at a high temperature. More preferably, the remote source isa remote plasma source that dissociates hydrogen-containing gas in aplasma that is initiated and sustained with energy in the form ofelectromagnetic radiation. In this application, electromagneticradiation is taken to mean any form of radiation resulting fromoscillating electromagnetic fields. Such radiation includes but is notlimited to all bands of the electromagnetic spectrum including longwave, radiofrequency, microwave, infrared, visible ultraviolet, x-rayand gamma ray. Still more preferably, the remote source dissociateshydrogen-containing gas with radiation having a frequency of betweenabout 100 kilohertz (kHz) and 100 gigahertz (GHz). A strike gas such asargon (Ar) or nitrogen (N₂) may optionally be supplied to the remoteplasma source to facilitate striking the plasma.

Two examples of such remote sources are shown in FIGS. 12 a and 12 b.The deposition chamber 15 generally includes a remote clean source 202for cleaning the chamber with nitrogen trifluoride (NF₃), as shown inFIG. 2. Such a remote clean sources can be coupled to the systemcontroller and configured to operate in response to instructionsembodied in a computer program. This same remote clean source 202 can beconfigured to selectively receive a hydrogen-containing gas for thepre-treatment described above.

FIG. 12 a depicts a remote RF plasma source 1200. Remote RF plasmasource 1200 generally comprises a remote chamber 1202 coupled to gassources 1204 via gas lines 1205. Remote chamber 1202 is fluidly coupledby a conduit 1207 to a process chamber such as chamber 15 depicted inFIGS. 1 a and 1 b. Gas sources 1204 provide hydrogen-containing gas toremote chamber 1202. Remote chamber 1202 includes gas deflectors 1206and an RF electrode 1208. Deflectors 1206 direct the flow of gas in aspiral flow pattern 1212 within remote chamber 1202. RF electrode 1208is coupled to an RF generator 1210. RF generator 1210 delivers energy inthe form of RF radiation to the hydrogen containing gas via RF electrode1208 Spiral pattern 1212 increases the residence time ofhydrogen-containing gas in remote chamber 1202 thereby facilitatingdissociation of free atomic hydrogen from the hydrogen containing gas.In one embodiment RF generator 1210 provides between 2000 and 5000 wattsof RF power, preferably 3000 watts at frequency of between 1 MHz and 100MHz, preferably about 13.56 MHz. NH₃ is provided to remote RF plasmasource 1200 at about 950 sccm. Argon is also provided to remote RFplasma source 1200 at about 1500 sccm. An example of a suitable remoteRF source 1200 is an ASTRON™ manufactured by Applied Science andTechnology (ASTeX), of Woburn Mass. Such a source is capable ofdissociating NH₃ with an efficiency of 95%.

FIG. 12 b depicts a remote microwave plasma source 1250. Remotemicrowave plasma source 1250 generally comprises a microwave transparentdischarge tube 1252 coupled to gas sources 1254 via gas lines 1255.Discharge tube 1252 is typically made from a dielectric material such asquartz. Discharge tube 1252 is fluidly coupled by a conduit 1253 to aprocess chamber such as chamber 15 depicted in FIGS. 1 a and 1 b. Gassources 1254 provide hydrogen-containing gas to discharge tube 1256.Discharge tube 1252 is situated within a tunable microwave cavity 1256.Microwave cavity 1256 is coupled to a microwave generator 1258 via amicrowave transmission line or waveguide 1260. Microwave cavity 1256generally includes fixed walls 1257 a and a movable wall 1257 b. Movablewall 1257 b moves longitudinally with respect to fixed walls 1257 athereby tuning cavity 1256 to optimize transfer of microwave power tothe hydrogen containing gas. In one embodiment the microwave generatorprovides between 1500 and 2500 watts, preferably about 2100 watts ofmicrowave power at frequency of between 1 and 5 GHz, preferably about2.2 GHz. An example of a suitable remote microwave source 1250 is aRemote Clean™ source manufactured by Applied Science and Technology(ASTeX), of Woburn Mass. Such a source is capable of dissociating NH₃with an efficiency of 99%.

In a preferred embodiment of the pre-treatment process, the remotemicrowave source operates at a frequency approximately 2.2 gigahertz anda power of 2100 Watts. NH₃ is provided to remote the microwave source at950 sccm. The substrate is generally at a temperature of 100° C. to 400°C. and the chamber wall is typically at a temperature of 65° C. Thepressure in the remote source is approximately 8 torr and the chamberpressure is approximately 5 torr.

While the present invention is initially developed pretreatment step1000 in the context of an organosilane/ozone carbon-doped silicon oxidefilm, pretreatment step 1000 is applicable to any type of film thatwould benefit from atomic hydrogen treatment of the underlying layer.

V. Post Deposition Treatment

After deposition, a silicon carbon or Si—O—C film is often quite porous.Consequently, the film tends to absorb moisture. The absorbed moisturegenerally degrades the properties of the film. In the case of a low-kfilm, moisture tends to increase the dielectric constant of the film andis detrimental to film adhesion. The porosity is normally reduced duringthe previously described thermal cure. However, if the cure is performedex-situ, the film is exposed for a time to moisture from the ambientatmosphere (e.g., the clean room atmosphere). The film may also tend toshrink during subsequent polymerization and curing processes.

Additional modifications to the above described deposition processprovide for a post deposition treatment to enhance adhesion of a low-kdielectric layer to a subsequently deposited layer and reduce shrinkage.The post-deposition treatment (step 1020 in FIG. 10) generally includesa densification step performed before removing the substrate fromvacuum. The densification involves heating the substrate in a reducingambient atmosphere to reduce shrinkage of the low-k dielectric layer.Suitable reducing environments include NH₃ and H₂. The densification canbe performed in the same chamber as the deposition, or a differentchamber. If done in a different chamber, however, the wafer ispreferably transferred to that chamber under vacuum controlledconditions.

In one embodiment of the post-deposition treatment the substrate isheated in an NH₃ ambient to between approximately 300 and 500° C.,preferably about 400° C. for between 1 and 5 minutes, preferably about1.5 minutes, at a pressure below atmospheric pressure. If the pressurein the chamber is above atmospheric pressure there is a possibility thegreater pressure might cause the chamber lid to open. Typically, thepressure is between about 200 and 700 torr, preferably about 600 torr.

The densification described above is not normally employed inembodiments where the substrate is cured without breaking vacuum afterdepositing the low-k film. While the present inventors have found postdeposition step 1020 to be particularly useful to stabilize low kozone/organosilance carbon-doped silicon oxide films deposited accordingto the present invention and that are subsequently cured in an ex-situprocess, step 1020 is a useful treatment for any film that is unstablein air. Such a densification is particularly useful for protecting lowtemperature deposited films that undergo an ex-situ cure. Such filmsinclude TMS-ozone films, spin on glass (SOG) and Black Diamond™. In thecase of Black Diamond™, the densification is performed in an oxygen (O₂)ambient to remove hydrogen from the film.

VI. Post-Cure Plasma Densification Treatment

Si—O—C low-k films that have been deposited in accordance with thepre-deposition, deposition, post deposition, and curing processesdescribed above are often subject to oxidizing environments in thecourse of subsequent processing. Such oxidizing processes include, butare not limited to, etching, photoresist strip and oxide cappingprocesses. The low-k film is typically a silicon-oxy-carbon structure.In an oxidizing environment the low-k film can react with oxygen andhydrogen to form carbon dioxide (CO₂) and water vapor (H₂O). Thereaction removes carbon from the film leading to shrinkage and increasein k-value.

The situation is illustrated in the Fourier transform infrared (FTIR)spectra depicted in FIGS. 13 a-13 d. FIG. 13 a depicts a first FTIRspectra 1302 for an as-deposited Si—O—C low-k film. Note the presence ofC—H and Si—C bonds in the spectra indicating the desired Si—O—Cstructure. To simulate the effect of an oxidizing environment duringprocessing, the as deposited film was subjected to an oxygen plasma for3 minutes at 400° C. The oxygen plasma produces active oxygen speciesthat attack the film. A second FTIR spectra 1304 taken after oxygenplasma treatment shows little or no C—H and Si—C bonds indicating theremoval of carbon from the film. The FTIR spectra in FIG. 13 b. showthat oxygen plasma also removes carbon from a post-cured Si—O—C film.Spectra 1306, for example, was taken on a post cured TMS-ozone depositedfilm. Spectra 1308 was taken on the same film after treatment in oxygenplasma for 3 minutes at 400° C.

FIG. 13 c depicts FTIR spectra from a similar experiment in which theas-deposited film was subjected to baking in an O₃ environment at 400°C. As in FIG. 13 a, a post deposition FTIR spectrum 1310 shows C—H andSi—C bonds while a post bake FTIR spectra 1312 does not. The O₃ bakeremoves carbon from the film, which is believed to cause a collapse ofthe film structure resulting in a shrinkage in film thickness. Thepost-O₃-bake film also exhibited increased refractive index and moistureabsorption. Furthermore, a post-cured film exhibited the same behavioras shown in post-cure spectra 1314 and post-bake spectra 1316 of FIG. 13d.

In addition to degradation of the cured film's properties, the filmtends to outgas during subsequent heating (e.g., during annealing). Theoutgassing can cause bubbles that lead to delamination of a subsequentlydeposited layer.

To overcome these problems, another embodiment of the method of thepresent invention includes a densification treatment after the film iscured. The densification process is an optional process that depends, toa certain extent, on the type of low-k film. For example, adensification step is not normally implemented for a barrier low-k(BLOK™) film since this type of film has a silicon carbide (Si—C)structure that is not normally subject to oxidation. The plasmadensification process is particularly useful for Si—O—C films depositedusing an organosilane. Typically the densification plasma is an RFplasma containing helium (He), nitrogen (N₂), or Argon (Ar).Alternatively an RF or remote microwave plasma containing NH₃ and O₂ maybe used. Preferably, the plasma is formed from a gaseous mixture of Heand N₂. Ar plasma is not normally if sputtering would be a problem.However, Ar plasma may be used if, for example, sputtering is a desiredeffect.

In one embodiment, a substrate containing a TMS-ozone deposited low-kfilm is cured in-situ at approximately 400° C. for between approximately3 and 30 minutes, preferably about 10 minutes. The cured film is thensubjected to N₂ plasma for approximately two minutes while the substrateis heated to between approximately 350 and 450° C., preferably about400° C. The chamber pressure is typically maintained at between about1.2 and 5.0 torr, preferably about 1.5 torr. The plasma is sustained byradiofrequency (RF) energy delivered at a power of between 500 and 900watts, preferably about 700 Watts and a frequency of between 100 KHz and100 MHz, preferably about 450 KHz. One example of a suitable chamber forthe densification process is a DxZ PECVD chamber manufactured by AppliedMaterials of Santa Clara, Calif. Such a chamber is described in U.S.Pat. No. 5,558,717.

FIG. 13 e depicts FTIR spectra taken for TMS/ozone deposited Si—O—C filmthat was treated with the densification described above following apost-deposition cure. Spectra 1318, taken for the as-deposited film,exhibits the C—H and Si—C bonds characteristic of the desired filmstructure. The as-deposited film was cured and then subjected todensification in an N₂ plasma. In this case, the substrate temperaturewas 250° C., and chamber pressure was 4.5 torr during plasmadensification. Nitrogen was provided at a flow rate of 2000 sccm. RFpower of 700 watts was provided at a frequency of 13.56 MHz. Spectra1320 was taken on the same film after the N₂ plasma treatment. Note thatthe C—H and Si—C bonds are little changed compared to as-depositedspectra 1318. The densified film was then subjected to a first oxygenplasma for 3 minutes at a substrate temperature of 250° C. Spectra 1322,taken after the first oxygen plasma treatment, shows little change inthe C—H and S₁—CH₃ bonds. The same film was then subjected to a secondoxygen plasma for 3 minutes at a substrate temperature of 400° C.Spectra 1224, taken after the second oxygen plasma treatment, againshows little change in the C—H and S₁—CH₃ bonds. Table I shows theeffect of the N₂ and oxygen plasma treatments on film properties.

TABLE I Shrinkage after Film Thickness (Å) initial cure (%) RefractiveIndex As-deposited 3716.2 1.428 Post-cure 3440.3 1.397 N₂ plasma treated3394.3 1.34 1.397 250° C. O₂ plasma 3287.4 4.44 1.396 400° C. O₂ plasma3249.3 5.55 1.396

As can be seen in FIG. 12 e, the plasma densification process stabilizesthe film and prevents removal of carbon in an oxidizing environment suchas etch and photoresist strip. Table I demonstrates that the N₂treatment has a negligible effect on the refractive index (and thereforek-value) of the film. Table I further demonstrates that the N₂densification process produces relatively little shrinkage of the postcured film.

Furthermore, the present inventors have discovered that if an overlyingcap layer is deposited over an ozone/organosilane film according to thepresent invention, densification treatment 1040 prevents delamination ofan overlying cap layer due to bubble formation. Bubbles may form with anundensified Si—O—C layer due to outgassing from the Si—O—C layer duringhigh temperature processes such as annealing. In an experiment, a low-kfilm was deposited on a substrate using TMS-ozone as described above.After deposition, the substrate was cured for 5 minutes at 400° C. Aftercuring, the substrate was subject to N₂ plasma for 2 minutes and thencapped with PE TEOS. The substrate exhibited no bubbling of the caplayer even after annealing at 450° C.

VII. Capping TMS-Ozone Deposited Layers

In some instances, the present inventors have found that Si—O—C filmsthat have been deposited in accordance with the pre-deposition,deposition, and post deposition and densification described above maystill be susceptible to cracking after curing as described above. Thisoccurs in spite of the fact that the observed stress, the k-value, andthe FTIR spectrum for the film do not change over time. The presentinventors have observed that the susceptibility of the film to crackingdepends upon the thickness of the deposited film and the length of timeto which the film is exposed to the ambient (air). A post-cured film6000 Å or less in thickness, that has not undergone plasmadensification, is typically stable, i.e. it does not crack after anindefinite period of time after exposure to ambient. At 8000 Å anundensified film cracks after about one week exposure. At 1.2 microns,and undensified film typically cracks upon removal from the chamber,i.e., upon exposure. Generally, the thicker the film, the sooner thefilm cracks. Densification also affects the thickness at which the filmcracks. For example, the present inventors have found that a post curedorganosilane deposited Si—O—C film that has not been densified in anitrogen plasma, as described above, cracks at thickness of 8000 Å ormore within about a week. A comparable film, that has undergone plasmadensification, is stable up to a thickness of about 1.2 microns. Atabout 1.6 microns thick, a plasma densified film cracks after about twodays. At 2 microns thickness, or greater, a densified film typicallycracks upon removal from the chamber.

To overcome this, another embodiment of the present invention includescapping the TMS-ozone deposited low-k film with a layer of oxide ornitride. It is believed that the if the cap layer is harder thanTMS-ozone low-k layer the cap layer physically holds the low-k filmtogether. The cap layer provides a barrier against moisture penetrationof the low-k film. The cap layer, typically a silicon oxide or siliconnitride, may be deposited by any conventional means. Preferably the caplayer is a silicon oxide deposited to a thickness of between 1000 Å and3000 Å by plasma enhanced chemical vapor deposition (PECVD) using aprecursor such as TEOS. Such a cap layer is referred to herein as a PETEOS layer. The inventors have found that a TMS-ozone film that has beenplasma densified and capped with a 1000 Å PE TEOS film is stable up to athickness of 1.6 microns. At about 2 microns thick, a densified andcupped film cracks after 3-4 days. Silicon nitride generally provides astronger cap layer and a better moisture barrier. Consequently, siliconnitride cap layers can be thinner, perhaps for example, or the order ofa few hundred angstroms.

In some applications, a cap layer might be undesirable. For example inprocesses that require a low interlayer capacitance, such as damasceneprocesses, a cap layer might not be used. The inventors have foundhowever that capping solves the problem of film cracking.

VIII. Exemplary Enhanced Deposition of an Si—O—C Layer

FIGS. 14 a-14 f depict detailed flow diagrams of the steps of anexemplary embodiment of the method of the present invention depicted inFIG. 10. In this exemplary embodiment, the substrate is pre-treatedusing a remote microwave plasma containing NH₃ in step 1000. The Si—O—Clayer is deposited with TMS-ozone using dual heat exchangers in step1010. The as-deposited Si—O—C layer is densified in a reducing ambientof NH₃ in step 1020 and furnace cured ex-situ in step 1030. In analternative embodiment, the Si—O—C film is cured in-situ anddensification step 1020 is omitted. The cured Si—O—C layer is densifiedin a nitrogen containing plasma in step 1040 and capped with PE TEOS instep 1050.

The flow diagram of FIG. 14 a shows the details of an exemplarypretreatment step, shown in FIG. 10 as step 1000. In the pre-treatmentprocess of FIG. 14 a. A wafer is inserted into the chamber at step 1401.Gas flows and temperatures are established in step 1402. NH₃ is suppliedto the remote microwave source at about 950 sccm. The pressure isstabilized at about 8 torr in the microwave source and 8 torr in thechamber. The pedestal is maintained at a temperature of approximately125° C. and the chamber wall is typically at a temperature ofapproximately 65° C. during pretreatment. In step 1403, the remotemicrowave source applies microwaves to the gases to ignite the remoteplasma. The microwave frequency is approximately 2.2 gigahertz andmicrowave power is about 2100 Watts. In step 1404, atomic hydrogenproduced in the plasma treats the substrate for between about 1 to 5minutes, preferably about 1.5 minutes. Finally, the gases and microwavesare shut off (step 1405).

FIG. 14 b is a flowchart of one embodiment of a thermal depositionprocess, shown in FIG. 10 as step 1010, that employs a process gas ofTMS, ozone and helium. This particular embodiment utilizes dual heatexchangers to separately control chamber wall temperature and chamberlid temperature. The process set forth in FIG. 14 b is for exemplarypurposes only and should not be considered limiting to the scope of thepresent claims. The pedestal and heat exchanger temperatures are set andstabilized prior to film deposition in step 1411. All three temperaturesare maintained approximately constant throughout deposition. In theabove example, the walls are maintained at about 60° C., the lid of thedeposition chamber is maintained at a temperature of about 25° C. andthe pedestal is maintained at a temperature of about 400° C. Thedeposition process is initiated, after a wafer has been loaded into thedeposition chamber, by flowing helium (8000 sccm) and oxygen (5000 sccm)gases while keeping the throttle valve fully open (step 1412) forseveral seconds to stabilize the gas flows. Ozone is not introduced atthis stage because the high reactivity of ozone.

Once the gas flow has stabilized, the throttle valve is partially closedand the pressure within the chamber is brought to the desired depositionpressure level in the presence of the helium and oxygen flows (step1413). Once the desired pressure level is reached and maintained for acouple of seconds, an ozone flow (5000 sccm) is substituted for theoxygen flow and a flow of TMS is initiated (500 sccm) to deposit acarbon-doped silicon oxide film (step 1414). Deposition step 1414continues until the carbon-doped silicon oxide layer reaches a desiredthickness and then the ozone flow is shut off (step 1415). The ozoneflow is switched off prior to the TMS flow in order to allow the TMS toreact with residual ozone in the gas phase. The TMS flow is then shutoff several seconds after the ozone flow (step 1416) and the depositionpressure is released by opening the throttle valve while maintaining thehelium flow (step 1417). Finally, all the gases are shut off (step1418).

The flow diagram of FIG. 14 c shows the details of an exemplarypost-deposition densification step, shown in FIG. 10 as step 1020. Inthe exemplary embodiment, this step is performed because the substrateis cured ex-situ in the following step. The exemplary post-depositiondensification begins at step 1421, by establishing gas flows andtemperatures. NH₃ is supplied at a pressure of about 600 torr and thesubstrate is heated to about 400° C. The substrate is treated for about90 seconds in step 1422. Gases pedestal heating are shut off and thepedestal allowed to cool in step 1423.

The flow diagram of FIG. 14 d shows the details of an exemplary furnacecure, shown in FIG. 10 as step 1030. In the exemplary embodiment, thesubstrate is removed from a vacuum environment and placed in a furnacein step 1431. Of course, multiple wafers may be placed in the furnacefor simultaneous curing. Substrate process throughput is generallyoptimized when as many substrates as possible are furnace cured at thesame time. An ambient atmosphere of nitrogen (N₂) is provided to thefurnace at step 1432. The furnace then heats the substrate to atemperature of about 400° C. for a period of about 30 minutes in step1433.

The flow diagram of FIG. 14 e shows the details of an exemplary in-situcure, shown in FIG. 10 as step 1030. Such a cure can be performed in achamber such as that depicted in FIGS. 1A-1F. The pedestal temperatureand gas flows of helium He and O₂ are established with the throttlevalve open in step 1434. He is supplied at about 6000 sccm and O₂ issupplied at about 3000 sccm. The pedestal temperature is set to about400° C. The presence of O₂ enhances shrinkage during the cure. In step1435, the throttle valve is partially closed to raise the pressure inthe chamber to about 450 torr. The substrate is then heated with thepedestal at a temperature of 400° C. and the chamber pressure at 450torr for about 10 minutes in step 1436. The flow of oxygen is shut offat step 1437 and the chamber is purged. The pressure is raised to about800 torr by further closing the throttle valve. In step 1438, thethrottle valve is fully opened. The helium flow is reduced to about 2000sccm and a flow of about 500 sccm of N₂ is introduced to the chamber.

The flow diagram of FIG. 14 f shows the details of an exemplarypost-cure plasma densification step, shown in FIG. 10 as step 1040. Theplasma densification may be performed in a processing chamber of thetype depicted in FIGS. 1A-1F. If the cure step preceding the plasmadensification was an in-situ cure, plasma densification may take placein the same chamber as the cure. If the cure step was a furnace cure,the post cured substrate is removed from the furnace and placed in aprocessing chamber in step 1441. A process gas of N₂ is supplied to thechamber in step 1442. The process gas is then ignited to form a plasmain step 1443. The substrate is then subjected to N₂ plasma forapproximately two minutes while the substrate is heated to about 400° C.in step 1444. The chamber pressure is maintained at about 1.5 torr. Theplasma is sustained by radio frequency (RF) energy delivered at a powerof about 700 Watts and a frequency of about 450 kHz. The RF power isturned off and the gas flows are stopped in step 1445.

The flow diagram of FIG. 14 g shows the details of an exemplary cappingstep, shown in FIG. 10 as step 1050. In the exemplary embodiment, thecap layer is deposited on the plasma densified Si—O—C layer in the samechamber as that used in the plasma densification step. Alternatively,the substrate containing the Si—O—C film may be transferred to adifferent chamber for capping. In step 1451, process gas flows and otherprocess conditions are established. Helium is provided at about 1000sccm. TEOS is provided at about 1050 milligrams/minute (mgm). Oxygen(O₂) is provided at about 1000 sccm. The chamber pressure is generallyabout 8.2 torr and the pedestal temperature about 400° C. In step 1452the process gases are energized to form a plasma. 1000 Watts of RF powerare supplied at a frequency of about 13.56 MHz. In step 1453 a siliconoxide cap layer is deposited using the plasma. Deposition proceeds untilthe cap layer has a thickness of about 2000 Å. In step 1454, RF power isturned off and the flow of process gases is stopped. The substrate maythen be removed from the chamber for further processing, such asphotoresist deposition, metal deposition, etc.

The methods described above can be readily incorporated into existingprocess recipes. For example, FIGS. 15 a-15 h depict one example of anIMD gap fill process incorporating the above method. In FIG. 15 a afirst metal layer 1502 of Al is deposited on an Si substrate 1500. Ananti-reflective coating of TiN 1504 is deposited on Al layer 1502. InFIG. 15 b a first photoresist layer 1506 is deposited on the TiN 1504.The walls of gaps 1508 are treated with free atomic hydrogen asdescribed above to reduce aluminum oxide. In FIG. 15 c TiN and Al layersare etched to form gaps 1508 using the patterned photoresist 1506. InFIG. 15 d A low-k TMS layer 1510 is deposited, cured and densified asdescribed above to fill gaps 1508. TMS layer 1510 is capped with PE TEOS1512. PE TEOS layer 1512 is planarized (e.g., using CMP) and coveredwith a second patterned photoresist 1514 in FIG. 15 e. PE TEOS and TMSlayers are then etched through second patterned photoresist layer 1514down to TiN layer 1504 to form vias 1516 as shown in FIG. 15 f. Afteretching, photoresist 1514 is stripped, e.g., by ashing in an oxidizingenvironment. Densification treatment 1040 protects PE TEOS and TMSlayers during etch and photoresist strip. Vias 1516 are filled with ametal such as tungsten to form interconnects 1518 as shown in FIG. 15 g.After planarization, a second metal layer 1520 and barrier layer 1522can be deposited over interconnects 1518 as shown in FIG. 15 h. Theprocess of FIGS. 15 b-15 h can then be repeated multiple times until thedesired integrated circuit structure is complete. Such a processintegration scheme is simple and involves relatively little complexitywith CMP, etch, and photoresist strip. Such a process does producerelatively high k values between the metal layers due to PE TEOS layer1512. Lower k values between the lines can be achieved, for example byeliminating the deposition of PE TEOS cap layer 1512.

A dual-damascene process integration scheme that utilizes the low-kTMS-ozone deposition method described herein is depicted in FIGS. 16a-16 h. The dual damascene process begins with the deposition of anoxide layer 1602 over a silicon substrate 1600 as shown in FIG. 16 a. Ahardmask layer 1604, e.g., silicon nitride (Si₃N₄), is deposited overoxide layer 1602. A first low-k TMS layer 1606 is deposited, cured anddensified as described above. First TMS layer 1606 is covered with apatterned photoresist layer 1608 during a first photolithography asshown in FIG. 16 b. In FIG. 16 c, a first etch forms a first set of gaps1610 in first TMS layer 1606 down to hardmask layer 1604. After thefirst etch, photoresist 1608 is stripped, e.g., by ashing in anoxidizing environment. Densification treatment 1040 protects TMS layer1606 during etch and photoresist strip. Gaps 1610 and first TMS layer1606 are then covered with a layer of metal, such as aluminum or copper.In the case of copper, a seed layer 1612 (FIG. 16 c) is deposited overgaps 1610 and first TMS layer 1606. A first bulk copper layer 1614 isdeposited to fill the gaps 1610 as shown in FIG. 16 d. Copper layer 1614is planarized, e.g., by CMP. Copper layer 1614 forms, e.g., a first setof metal lines in an interconnect structure.

After planarization, of copper 1614, a second hardmask layer 1616, asecond TMS 1618 layer, a third hardmask layer 1620 and third TMS layer1622 are deposited as shown in FIG. 16 e. A second lithography and etchforms vias 1624 through layers 1616, 1618, 1620 and 1622 down to copperlayer 1614 as shown in FIG. 16 f. In FIG. 16 g, a third lithography andetch forms a second set of gaps 1626. Gaps 1626 define a second set ofmetal lines and vias 1624 define a set of interconnects between thesecond set of metal lines and the first set of metal lines defined bygaps 1610 and copper layer 1614. Vias 1624 and gaps 1626 are then filledwith a second bulk copper layer 1628 as shown in FIG. 16 h. Theresulting structure is then annealed and planarized.

Damascene processes are used in devices that use copper interconnectsbecause there is currently no acceptable way to etch copper. Structuresformed by damascene processes do not require a gap-fill dielectric andgenerally provide lower RC delays than similar structures formed usingaluminum metal lines. Furthermore, higher deposition rates may be usedin damascene processes since gap-fill is not an issue.

Having fully described several embodiments of the present invention,many other equivalent or alternative methods of depositing the lowdielectric constant oxide layer according to the present invention willbe apparent to those skilled in the art. These alternatives andequivalents are intended to be included within the scope of the presentinvention.

1. A method of depositing a carbon-doped silicon oxide layer upon asubstrate, the method comprising: providing the substrate to adeposition chamber; flowing a process gas comprising an organosiliconprecursor having at least one silicon-carbon bond and an oxygen sourceinto the deposition chamber during a first deposition step whilemaintaining the deposition chamber at a chamber pressure level and otherprocess conditions suitable for depositing carbon-doped silicon oxidematerial over the substrate using a thermal chemical vapor depositionprocess; and during a second deposition step subsequent to the firstdeposition step, flowing a process gas comprising an organosiliconprecursor having at least one silicon-carbon bond and an oxygen sourceinto the deposition chamber while maintaining the deposition chamber atprocess conditions suitable for depositing carbon-doped silicon oxidematerial over the substrate, wherein the process conditions of thedeposition chamber during the second deposition step include a chamberpressure level at least 50 Torr less than the chamber pressure level ofthe first deposition step; wherein the chamber pressure level during thefirst deposition step is maintained within a range of between about 200to 700 Torr, the chamber pressure level during the second depositionstep is maintained within a range of between about 50 to 150 Torr and atemperature of the substrate is increased by at least about 25° Celsiusfrom the first deposition step to the second deposition step.
 2. Themethod set forth in claim 1 wherein the oxygen source in the firstdeposition step comprises ozone.
 3. The method set forth in claim 2wherein the oxygen source in both the first and second deposition stepscomprises ozone and wherein at the end of the carbon-doped silicon oxidedeposition process the flow of the organosilicon precursor is shut-offafter shutting off the flow of ozone.
 4. The method set forth in claim 1wherein the process gas in both the first and second deposition stepscomprises trimethylsilane, ozone, oxygen and an inert gas.
 5. The methodset forth in claim 1 wherein the process gas in both the first andsecond deposition steps comprises tetramethylsilane, ozone, oxygen andan inert gas.
 6. The method set forth in claim 1 wherein the depositedcarbon-doped silicon oxide film has a density of less than or equal toabout 1.2 g/cm³.
 7. The method set forth in claim 1 wherein the firstdeposition step is optimized for gapfill while the second depositionstep is optimized for deposition rate.
 8. The method set forth in claim1 wherein, prior to initiating a flow of the process gas in the firstdeposition step, a flow of an inert gas and oxygen is introduced intothe deposition chamber, then after the chamber pressure level of thefirst deposition step is reached, a flow of ozone is substituted for theflow of oxygen.
 9. The method set forth in claim 1 wherein the processgas in both the first and second deposition steps further comprises oneor more dopant sources selected from boron and phosphorus sources.